1. Field of the Invention
The present invention relates to an image formation apparatus, such as a photocopier, and a preparation operation execution method. In particular, the present invention relates to an image formation apparatus and a preparation operation execution method for (i) executing a preparation operation including a plurality of different processes, and (ii) upon completion of the preparation operation, shifting to a ready state in which an image formation operation is executable.
2. Related Art
A tandem color image formation apparatus is, for example, configured in the following manners: image forming units for different colors are arranged along an intermediate transfer belt; the image forming units transfer toner images formed on the photosensitive drums onto the intermediate transfer belt as a multiple transfer; the toner images of different colors, which have been transferred and layered on the intermediate transfer belt, are collectively transferred to a recording sheet; and the toner images on the recording sheet are fixed onto the recording sheet by a fixer heating and pressing the toner images.
Once the power is turned on, the above image formation apparatus normally executes a preparation operation until it shifts to a ready state in which image formation is executable.
The preparation operation includes, for example, a warm-up for increasing the temperature of the fixer to a temperature required to perform the fixing (a target temperature), and image stabilization control such as color registration correction.
The warm-up is to increase temperatures of a fixing roller and a pressure roller provided in the fixer by, while heating a heater of the fixer, rotating the fixing roller and the pressure roller at a constant speed with use of a fixing motor, such that the heat from the fixing heater is transferred all over the fixing roller and the pressure roller.
The color registration correction is to (i) form a registration pattern for each color on the intermediate transfer belt, while rotating the intermediate transfer belt at a constant speed with use of a main motor, (ii) detect positions of the formed registration patterns with use of a sensor or the like, (iii) calculate an amount of position shift of each color with reference to the detected positions of the registration patterns, and (iv) when performing image formation next time, correct an image write position of each color in accordance with the amount of position shift of each color.
Upon completion of the preparation operation such as the warm-up and the image stabilization control, the image formation apparatus shifts to the ready state. Hence, the longer it takes to complete the preparation operation, the more delayed the shift to the ready state. The more delayed the shift to the ready state, the longer a user has to wait. It is thereby desirable to complete the preparation operation as promptly as possible.
One method to complete the preparation operation as promptly as possible is to, for example, rapidly accelerate a motor used for a process of the preparation operation by initiating the motor with a high voltage applied thereto (hereinafter, referred to as “a high-speed initiation”). This way, the motor is promptly initiated, thus reducing a time period from the initiation until the motor is stabilized to rotate at a constant speed.
With respect to the color registration correction, the photosensitive drums and the intermediate transfer belt need to be stabilized to rotate at a constant speed at the time of forming the registration pattern for each color. Accordingly, if it takes time to stabilize the photosensitive drums and the intermediate transfer belt to rotate at a constant speed, the following disadvantages will follow: time of forming each registration pattern is delayed; time of executing the subsequent pattern detection and calculating the amount of position shift of each color is delayed; and completion of the color registration correction is delayed.
Meanwhile, with respect to the warm-up, it takes time to rotate the fixing roller and the pressure roller at a required rotation frequency. This extends a time period required between a start and completion of the warm-up.
Therefore, if the main motor and the fixing motor are initiated at the same time by the high-speed initiation, the color registration correction and the warm-up can be executed in parallel in a short amount of time.
However, execution of the high-speed initiation increases a peak value of a supplied power compared to execution of the normal initiation. Thus, in order to cause the high-speed initiation of the two motors at the same time, a power unit needs to have a significantly larger capacitance, which will lead to a cost increase. Moreover, the image formation apparatus needs to comply with its rated power consumption. Accordingly, if the capacitance of each motor is significantly increased, then it will be necessary to suppress an amount of power supplied to constituent elements other than the motors, so as to maintain the total power consumption equal to or below the rated power consumption.
One method to cause the high-speed initiation of the two motors while suppressing power consumption is to cause the high-speed initiation of the two motors at different timings. This method requires a less amount of power than an amount of power required to cause the high-speed initiation of the two motors at the same time. However, when a plurality of preparation processes including the warm-up and the color registration correction are executed in parallel—e.g., when the main motor is initiated by the high-speed initiation to start the color registration correction during the warm-up (while the fixing motor is being driven), the power supplied during the high-speed initiation of the main motor is added to the power supplied to the fixing motor. This will increase a peak value of the total power consumption, with the result that the power unit is forced to have a larger capacitance.
To simply suppress the capacitance, the color registration correction could be started, for example, after completion of the warm-up. This way, a peak value of the total power consumption can be suppressed because other motors are not driven at the time of initiating the main motor by the high-speed initiation. This, however, is not parallel processing; therefore, it takes a large amount of time to complete the preparation process.
Such a problem could occur not only in a case where a plurality of motors are driven but also in a case where only one motor is driven—e.g., in a case where the high-speed initiation of the main motor and supply of power to the fixing heater are executed at the same time immediately after the power-on. In this case, as the power supplied for the high-speed initiation is added to the power supplied to the fixing heater, the power unit needs to have a larger capacitance.